d06

day06/d06p2.swift

@@ -0,0 +1,112 @@
+import Foundation
+
+enum Direction : Hashable {
+    case n, s, e, w
+    func turnRight() -> Direction {
+        let map: [Direction: Direction] = [.n: .e, .s: .w, .e: .s, .w: .n]
+        return map[self]!
+    }
+    func asChar() -> Character {
+        let map: [Direction: Character] = [.n: "^", .s: "v", .e: ">", .w: "<"]
+        return map[self] ?? "?"
+    }
+}
+
+struct GuardPos : Hashable {
+    let x: Int
+    let y: Int
+    let dir: Direction
+    func turnRight() -> GuardPos {
+        return GuardPos(x: x, y: y, dir: dir.turnRight())
+    }
+    func move() -> GuardPos {
+        switch dir {
+        case Direction.n:
+            return GuardPos(x: x-1, y: y, dir: dir)
+        case Direction.s:
+            return GuardPos(x: x+1, y: y, dir: dir)
+        case Direction.e:
+            return GuardPos(x: x, y: y+1, dir: dir)
+        case Direction.w:
+            return GuardPos(x: x, y: y-1, dir: dir)
+        }
+    }
+}
+
+struct Map {
+    var obst: [[Bool]]
+    var patrol: GuardPos
+    var visited: Set<GuardPos>
+    var done = false
+    var looped = false
+
+    func print() {
+        for (i, row) in obst.enumerated() {
+            Swift.print(String(row.enumerated().map { j, c in
+                (i == patrol.x && j == patrol.y) ?
+                    patrol.dir.asChar() : (c ? "#" : ".")
+            }))
+        }
+    }
+
+    mutating func step() {
+        let next = patrol.move()
+        if next.x < 0 || next.x >= obst.count
+           || next.y < 0 || next.y >= obst[0].count {
+            done = true
+        } else if obst[next.x][next.y] {
+            patrol = patrol.turnRight()
+        } else if visited.contains(next) {
+            looped = true
+            done = true
+        } else {
+            visited.insert(next)
+            patrol = next
+        }
+    }
+
+    func addObst(x: Int, y: Int) -> Map? {
+        if obst[x][y] {
+            return nil
+        }
+        var newObst = obst
+        newObst[x][y] = true
+        return Map(
+            obst: newObst, patrol: patrol,
+            visited: visited, done: done, looped: looped
+        )
+    }
+}
+
+func readInput(_ filePath: String) throws -> Map {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    let rows = content.split(separator: "\n").map(Array.init)
+    let (patrolX, patrolY) = rows.map {
+        $0.enumerated().compactMap { j, cell in cell == "^" ? j : nil }
+    }.enumerated().compactMap { $1.count > 0 ? ($0, $1[0]) : nil }[0]
+    let initPatrol = GuardPos(x: patrolX, y: patrolY, dir: Direction.n)
+    return Map(
+        obst: rows.map { $0.map { $0 == "#" } },
+        patrol: initPatrol,
+        visited: [initPatrol]
+    )
+}
+
+var map = try readInput(CommandLine.arguments[1])
+var count = 0
+for x in 0..<map.obst.count {
+    for y in 0..<map.obst[x].count {
+        print("Trying \(x), \(y)...")
+        if var newMap = map.addObst(x: x, y: y) {
+            while !newMap.done {
+                newMap.step()
+            }
+            if newMap.looped {
+                count += 1
+                print("!!!!!!!!")
+            }
+        }
+    }
+}
+print(count)
+